The invention relates to an electrical machine. From U.S. Pat. No. 6,163,128, a method for triggering electrical machines is known, by which electrical machines can be operated in the field attenuation mode. This reference does disclose that synchronous machines with a permanent-magnetically excitable rotor and a stator winding can be triggered in this way. However, further details of the electrical machine are not disclosed.
The electrical machine of the invention has the advantage that because of the special embodiment of the stator, the primary-field inductance is especially high and is therefore especially well suited for a field attenuation mode. With this winding geometry, the short-circuit current can be reduced so far that It is on the order of magnitude of the rated current end thus makes a theoretically infinite field attenuation range possible. The zero inductance of the machine becomes vanishingly small in this arrangement.
To enable a tooth of the stator to utilize the full flux of a permanent magnet or of the rotor, it is provided that the coil width of one coil be no greater than one pole pitch.
In principle, open slots with a minimum opening of one-third of the pole pitch are then present. As a result, either the winding technology is simplified, or prefabricated coils can be inserted into the open slots.
By the provisions recited in the dependent claims, advantageous refinements of the electrical machine of the main claim are possible.
The field-oriented regulation means that the machine is given the especially favorable performancexe2x80x94and in particular the regulabilityxe2x80x94of a direct-current machine. As a result, the field-forming longitudinal current and the torque-forming transverse current can be regulated separately from one another, and the machine can no longer tilt.
In permanently excited machines, in the fundamental rpm range the longitudinal current in the machine is regulated to zero. As a result, the machine generates the required torque at the minimum current and thus with the least machine losses.
As a result of the field attenuation mode, the electrical machine is possible above an rpm at which the terminal voltage of the machine reaches the maximum value of the inverter voltage.
By providing one coil side in each slot with otherwise the same dimensions, the inductance of the machine can be increased further, so that a lower field attenuation current is needed, and as a result the load on the machine drops.
If a coolant medium is passed through at least one slot, the result is especially good, effective cooling of the coils. Especially effective cooling is attained if cooling conduits for coolant fluid are accommodated here, which by direct or indirect contact with the copper conductors dissipate the heat directly.
If the machine is embodied such that an air gap between the rotor and one tooth of the stator is widened in the direction of the peripheral ends of the tooth, then the resting moment between the rotor and the stator is reduced. As a result of the resting moment, the torque course between the rotor and the stator is uneven, resulting in low-frequency oscillations that cause vibration of the electrical machine and adjacent components. Accordingly, reducing the resting moment leads to an improvement in travel comfort and a smoother torque course. Furthermore, however, the reduced resting moment prevents high-frequency oscillations and attendant noises. If the tooth width of an individual tooth of the stator is embodied in the circumferential direction with between two-thirds of a pole pitch and one full pole pitch, then by way of this provision the resting moment, with its attendant disadvantages, is avoided.